${\displaystyle \varphi (x;a,b)={\frac {\Gamma (a+b)}{\Gamma (a)\Gamma (b)}}x^{a-1}(1-x)^{b-1}}$
where ${\displaystyle a}$ and ${\displaystyle b}$ are the parameters of the distribution and ${\displaystyle \Gamma (z)}$ is the gamma function.